Brown carbon aerosol in the North American continental troposphere: sources, abundance, and radiative forcing

Abstract. Chemical components of organic aerosol (OA) selectively absorb light at short wavelengths. In this study, the prevalence, sources, and optical importance of this so-called brown carbon (BrC) aerosol component are investigated throughout the North American continental tropospheric column during a summer of extensive biomass burning. Spectrophotometric absorption measurements on extracts of bulk aerosol samples collected from an aircraft over the central USA were analyzed to directly quantify BrC abundance. BrC was found to be prevalent throughout the 1 to 12 km altitude measurement range, with dramatic enhancements in biomass-burning plumes. BrC to black carbon (BC) ratios, under background tropospheric conditions, increased with altitude, consistent with a corresponding increase in the absorption Ångström exponent (AAE) determined from a three-wavelength particle soot absorption photometer (PSAP). The sum of inferred BC absorption and measured BrC absorption at 365 nm was within 3 % of the measured PSAP absorption for background conditions and 22 % for biomass burning. A radiative transfer model showed that BrC absorption reduced top-of-atmosphere (TOA) aerosol forcing by ~ 20 % in the background troposphere. Extensive radiative model simulations applying this study background tropospheric conditions provided a look-up chart for determining radiative forcing efficiencies of BrC as a function of a surface-measured BrC : BC ratio and single scattering albedo (SSA). The chart is a first attempt to provide a tool for better assessment of brown carbon's forcing effect when one is limited to only surface data. These results indicate that BrC is an important contributor to direct aerosol radiative forcing.

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Brown carbon aerosol in the North American continental troposphere: sources, abundance, and radiative forcing

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-15-5959-2015 ◽

2015 ◽

Vol 15 (5) ◽

pp. 5959-6007 ◽

Cited By ~ 5

Author(s):

J. Liu ◽

E. Scheuer ◽

J. Dibb ◽

G. S. Diskin ◽

L. D. Ziemba ◽

...

Keyword(s):

Biomass Burning ◽

North American ◽

Radiative Forcing ◽

Single Scattering ◽

Measurement Range ◽

Radiative Transfer Model ◽

Chemical Components ◽

Transfer Model ◽

Brown Carbon ◽

The North

Abstract. Chemical components of organic aerosol selectively absorb light at short wavelengths. In this study, the prevalence, sources, and optical importance of this so-called brown carbon (BrC) aerosol component are investigated throughout the North American continental tropospheric column during a summer of extensive biomass burning. Spectrophotometric absorption measurements on extracts of bulk aerosol samples collected from an aircraft over the central USA were analyzed to directly quantify BrC abundance. BrC was found to be prevalent throughout the 1 to 12 km altitude measurement range, with dramatic enhancements in biomass burning plumes. BrC to black carbon (BC) ratios, under background tropospheric conditions, increased with altitude, consistent with a corresponding increase in the Absorption Ångström Exponent (AAE) determined from a 3-wavelength Particle Soot Absorption Photometer (PSAP). The sum of inferred BC absorption and measured BrC absorption at 365 nm was within 3% of the measured PSAP absorption for background conditions and 22% for biomass burning. A radiative transfer model showed that BrC absorption reduced top of atmosphere aerosol forcing by ~20% in the background troposphere. Extensive radiative model simulations applying this studies background tropospheric conditions provided a look-up chart for determining radiative forcing efficiencies of BrC as a function of surface-measured BrC–BC ratio and single scattering albedo (SSA). The chart is a first attempt to provide a tool for better assessment of brown carbon's forcing effect when one is limited to only surface data. These results indicate that BrC is an important component of direct aerosol radiative forcing.

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Estimation of Surface and Top-of-Atmosphere Shortwave Irradiance in Biomass-Burning Regions during SCAR-B

Journal of Applied Meteorology ◽

10.1175/1520-0450-39.10.1742 ◽

2000 ◽

Vol 39 (10) ◽

pp. 1742-1753 ◽

Cited By ~ 29

Author(s):

Sundar A. Christopher ◽

Xiang Li ◽

Ronald M. Welch ◽

Jeffrey S. Reid ◽

Peter V. Hobbs ◽

...

Keyword(s):

Radiative Transfer ◽

Biomass Burning ◽

Optical Thickness ◽

Radiative Forcing ◽

Wavelength Dependence ◽

Single Scattering ◽

Radiative Transfer Model ◽

Transfer Model ◽

Aerosol Radiative Forcing ◽

Mean Square Errors

Abstract Using in situ measurements of aerosol optical properties and ground-based measurements of aerosol optical thickness (τs) during the Smoke, Clouds and Radiation—Brazil (SCAR-B) experiment, a four-stream broadband radiative transfer model is used to estimate the downward shortwave irradiance (DSWI) and top-of-atmosphere (TOA) shortwave aerosol radiative forcing (SWARF) in cloud-free regions dominated by smoke from biomass burning in Brazil. The calculated DSWI values are compared with broadband pyranometer measurements made at the surface. The results show that, for two days when near-coincident measurements of single-scattering albedo ω0 and τs are available, the root-mean-square errors between the measured and calculated DSWI for daytime data are within 30 W m−2. For five days during SCAR-B, however, when assumptions about ω0 have to be made and also when τs was significantly higher, the differences can be as large as 100 W m−2. At TOA, the SWARF per unit optical thickness ranges from −20 to −60 W m−2 over four major ecosystems in South America. The results show that τs and ω0 are the two most important parameters that affect DSWI calculations. For SWARF values, surface albedos also play an important role. It is shown that ω0 must be known within 0.05 and τs at 0.55 μm must be known to within 0.1 to estimate DSWI to within 20 W m−2. The methodology described in this paper could serve as a potential strategy for determining DSWI values in the presence of aerosols. The wavelength dependence of τs and ω0 over the entire shortwave spectrum is needed to improve radiative transfer calculations. If global retrievals of DSWI and SWARF from satellite measurements are to be performed in the presence of biomass-burning aerosols on a routine basis, a concerted effort should be made to develop methodologies for estimating ω0 and τs from satellite and ground-based measurements.

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Greenhouse effects of aircraft emissions as calculated by a radiative transfer model

Annales Geophysicae ◽

10.1007/s00585-995-0413-4 ◽

1995 ◽

Vol 13 (4) ◽

pp. 413-418 ◽

Cited By ~ 29

Author(s):

J. P. F. Fortuin ◽

R. van Dorland ◽

W. M. F. Wauben ◽

H. Kelder

Keyword(s):

Water Vapor ◽

Radiative Transfer ◽

Indirect Effect ◽

Radiative Forcing ◽

Combustion Products ◽

Ozone Production ◽

Radiative Transfer Model ◽

Transfer Model ◽

Aircraft Emissions ◽

The North

Abstract. With a radiative transfer model, assessments are made of the radiative forcing in northern mid-latitudes due to aircraft emissions up to 1990. Considered are the direct climate effects from the major combustion products carbon dioxide, nitrogen dioxide, water vapor and sulphur dioxide, as well as the indirect effect of ozone production from NOx emissions. Our study indicates a local radiative forcing at the tropopause which should be negative in summer (–0.5 to 0.0 W/m2) and either negative or positive in winter (–0.3 to 0.2 W/m2). To these values the indirect effect of contrails has to be added, which for the North Atlantic Flight Corridor covers the range –0.2 to 0.3 W/m2 in summer and 0.0 to 0.3 W/m2 in winter. Apart from optically dense non-aged contrails during summer, negative forcings are due to solar screening by sulphate aerosols. The major positive contributions come from contrails, stratospheric water vapor in winter and ozone in summer. The direct effect of NO2 is negligible and the contribution of CO2 is relatively small.

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Exploring the observational constraints on the simulation of brown carbon

10.5194/acp-2017-655 ◽

2017 ◽

Author(s):

Xuan Wang ◽

Colette L. Heald ◽

Jiumeng Liu ◽

Rodney J. Weber ◽

Pedro Campuzano-Jost ◽

...

Keyword(s):

Optical Properties ◽

Biomass Burning ◽

Transport Model ◽

Model Simulation ◽

Radiative Transfer Model ◽

Transfer Model ◽

Observational Constraints ◽

Radiative Effect ◽

Brown Carbon ◽

Direct Measurements

Abstract. Organic aerosols (OA) that strongly absorbs solar radiation in the near-UV are referred to as brown carbon (BrC). However the sources, evolution, and optical properties of BrC remain highly uncertain, and contribute significantly to uncertainty in the estimate of the global direct radiative effect (DRE) of aerosols. Previous modeling studies of BrC optical properties and DRE have been unable to fully evaluate model performance due to the lack of direct measurements of BrC absorption. In this study, we develop a global model simulation (GEOS-Chem) of BrC and test it against BrC absorption measurements from two aircraft campaigns in the continental U.S. (SEAC4RS and DC3). To our knowledge, this is the first study to compare simulated BrC absorption with direct ambient measurements. We show that the BrC absorption properties from biomass burning estimated based on previous laboratory measurements overestimate the aircraft measurements of ambient BrC absorption. In addition, applying a photochemical scheme to simulate bleaching/degradation of BrC improves model skill. The airborne observations are consistent with a mass absorption coefficient (MAC) of freshly emitted biomass burning OA of 0.57 m2 g−1 at 365 nm with an absorption Ångström exponents (AAE) = 3.1 for 300 & 600 wavelengths pair, coupled with a 1 day whitening e-folding time. Using the GEOS-Chem chemical transport model integrated with the RRTMG radiative transfer model, we estimate that the top-of-atmosphere all-sky direct radiative effect (DRE) of OA is −0.350 Wm−2, 10 % higher than that without consideration of BrC absorption. Therefore, our best estimate of the absorption DRE of BrC is +0.042 Wm−2. We suggest that the DRE of BrC has been overestimated previously due to the lack of observational constraints from direct measurements and omission of the effects of photochemical whitening.

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Feasibility of Ceilometers Data to Estimate Radiative Forcing Values: Application to Different Conditions around the COVID-19 Lockdown Period

Remote Sensing ◽

10.3390/rs12223699 ◽

2020 ◽

Vol 12 (22) ◽

pp. 3699

Author(s):

Ruben Barragan ◽

Francisco Molero ◽

María José Granados-Muñoz ◽

Pedro Salvador ◽

Manuel Pujadas ◽

...

Keyword(s):

Radiative Forcing ◽

Strong Dependence ◽

Atmospheric Model ◽

Single Scattering ◽

Short Wave ◽

Cooling Effect ◽

Radiative Transfer Model ◽

Transfer Model ◽

Heating Effect ◽

Global Atmospheric Model

In this study, the feasibility of using ceilometer signals to retrieve radiative forcing values is evaluated. The Global Atmospheric Model (GAME) radiative transfer model is used to estimate the shortwave and longwave radiative forcing using an aerosol parameterization based on AERONET data and vertical profiles from a Lufft CHM-15k Nimbus ceilometer. First, eight cases confirmed as dusty days are analyzed to check the feasibility of using ceilometer profiles to feed GAME. The obtained radiative forcing estimates are in good agreement with the literature showing negative values in the short wave (SW) (cooling effect) and positive values in the long wave (LW) (heating effect), both at all levels. As in the literature, radiative forcing estimates show a strong dependence on variations in the aerosol optical depth (AOD), solar zenith angle (θz), surface temperature (ST), and single scattering albedo at 440 nm (SSA440). Thus, GAME can be fed using ceilometer measurements obtaining reliable results. Then, as the temporal evolution of the AOD440 between 27 January and 15 June compared to the 6-year weekly AERONET AOD440 average (from 2014 to 2019) shows a decrease because of the lockdown imposed in Spain due to the COVID-19, a total of 37 radiative forcing calculations without African dust, divided into 8 scenarios, are performed in order to check the effect of the lockdown measures in the radiative forcing. It is shown that the decrease in the AOD, during the lockdown, caused a decrease in the cooling effect in the SW spectral range at all levels. Besides, the increase in the ST increased the heating effect of the aerosols in the LW at the top of the atmosphere and the presence of pollution and absorbing particles (SSA440 < 0.90) caused an increase of the heating effect in the LW at the surface. Therefore, the observed variations in the radiative forcing estimates before and during the lockdown are directly related with the decrease in emissions of aerosols related to human activities.

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Interpreting the Ultraviolet Aerosol Index observed with the OMI satellite instrument to understand absorption by organic aerosols: implications for atmospheric oxidation and direct radiative effects

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-15-27405-2015 ◽

2015 ◽

Vol 15 (19) ◽

pp. 27405-27447

Author(s):

M. S. Hammer ◽

R. V. Martin ◽

A. van Donkelaar ◽

V. Buchard ◽

O. Torres ◽

...

Keyword(s):

Radiative Transfer ◽

South America ◽

Biomass Burning ◽

Southern Africa ◽

Radiative Forcing ◽

Transport Model ◽

Organic Aerosol ◽

Radiative Transfer Model ◽

Transfer Model ◽

Aerosol Index

Abstract. Satellite observations of the Ultraviolet Aerosol Index (UVAI) are sensitive to absorption of solar radiation by aerosols; this absorption affects photolysis frequencies and radiative forcing. We develop a global simulation of the UVAI using the 3-D chemical transport model GEOS-Chem coupled with the Vector Linearized Discrete Ordinate Radiative Transfer model (VLIDORT). The simulation is applied to interpret UVAI observations from the Ozone Monitoring Instrument (OMI) for the year 2007. Simulated and observed values are highly consistent in regions where mineral dust dominates the UVAI, but a large negative bias (−0.32 to −0.97) exists between simulated and observed values in biomass burning regions. We determine effective optical properties for absorbing organic aerosol, known as brown carbon (BrC), and implement them into GEOS-Chem to better represent observed UVAI values over biomass burning regions. The addition of absorbing BrC decreases the mean bias between simulated and OMI UVAI values from −0.57 to −0.09 over West Africa in January, from −0.32 to +0.0002 over South Asia in April, from −0.97 to −0.22 over southern Africa in July, and from −0.50 to +0.33 over South America in September. The spectral dependence of absorption after adding BrC to the model is broadly consistent with reported observations for biomass burning aerosol, with Absorbing Angstrom Exponent (AAE) values ranging from 2.9 in the ultraviolet (UV) to 1.3 across the UV-Near IR spectrum. We assess the effect of the additional UV absorption by BrC on atmospheric photochemistry by examining tropospheric hydroxyl radical (OH) concentrations in GEOS-Chem. The inclusion of BrC decreases OH by up to 35 % over South America in September, up to 25 % over southern Africa in July, and up to 20 % over other biomass burning regions. Global annual mean OH concentrations in GEOS-Chem decrease due to the presence of absorbing BrC, increasing the methyl chloroform lifetime from 5.62 to 5.68 years, thus reducing the bias against observed values. We calculate the direct radiative effect (DRE) of BrC using GEOS-Chem coupled with the radiative transfer model RRTMG (GC-RT). Treating organic aerosol as containing absorbing BrC rather than as primarily scattering changes global annual mean all-sky top of atmosphere (TOA) DRE by +0.05 W m-2 and all-sky surface DRE by −0.06 W m-2. Regional changes of up to +0.5 W m-2 at TOA and down to −1 W m-2 at the surface are found over major biomass burning regions.

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A case study on biomass burning aerosols: effects on solar UV irradiance, retrieval of aerosol single scattering albedo

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-8-17987-2008 ◽

2008 ◽

Vol 8 (5) ◽

pp. 17987-18005 ◽

Cited By ~ 1

Author(s):

A. Bagheri ◽

B. Kjeldstad ◽

B. Johnsen

Keyword(s):

Radiative Transfer ◽

Uv Radiation ◽

Biomass Burning ◽

Single Scattering ◽

Single Scattering Albedo ◽

The Arctic ◽

Radiative Transfer Model ◽

Transfer Model ◽

Uv Irradiance ◽

Surface Measurements

Abstract. The aerosol optical depth (AOD) from biomass burning aerosols from eastern Europe was measured in Trondheim, Norway (63.43° N , 10.43° E) in May 2006. The event was observed as far as the Arctic. In the first part of this paper, the surface measurements of direct and global UV radiation (and retrieved AOD) are used to simulate the data using a radiative transfer model. Measured and simulated data were used to study the effect of biomass aerosol on the levels of surface UV radiation. We found reductions of up to 31%, 15% and 2% in direct, global and diffuse surface UV irradiance (at 350 nm, SZA=50°±0.5°) as compared to typical aerosol conditions. In the second part of our study, surface measurements of global and direct irradiance at five wavelength in UVB and UVA (305, 313, 320, 340 and 380 nm) were coupled with a radiative transfer model to produce values of aerosol single scattering albedo, ω. The aerosol single scattering albedo for biomass aerosols is compared to ω for background aerosols. The values of ω for biomass aerosols were 0.76 at 305 nm, 0.75 at 313 nm, 0.79 at 320 nm, 0.72 at 340 nm and 0.80 at 380 nm.

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Aerosol radiative forcing during African desert dust events (2005–2010) over South-Eastern Spain

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-12-6593-2012 ◽

2012 ◽

Vol 12 (3) ◽

pp. 6593-6622 ◽

Cited By ~ 4

Author(s):

A. Valenzuela ◽

F. J. Olmo ◽

H. Lyamani ◽

M. Antón ◽

A. Quirantes ◽

...

Keyword(s):

Radiative Transfer ◽

Radiative Forcing ◽

Single Scattering ◽

Radiative Transfer Model ◽

Transfer Model ◽

Aerosol Radiative Forcing ◽

Desert Dust ◽

Aerosol Parameter ◽

Dust Events ◽

Aerosol Radiative

Abstract. The instantaneous values of the aerosol radiative forcing (ARF) at the surface and the top of the atmosphere (TOA) were calculated during desert dust events occurred at Granada (Southeastern Spain) from 2005 to 2010. For that, the SBDART radiative transfer model was utilized to simulate the global irradiance values (0.3–2.8 μm) at the surface and TOA using as input the aerosol properties derived from a CIMEL sun-photometer measurements and an inversion methodology that uses the sky radiance measurements in principal plane configuration and non-spherical particle shapes approximation. The SBDART modeled global irradiances at surface have been successfully validated against experimental measurements obtained by CM-11 pyranometer, indicating the reliability of the radiative transfer model used in this work for the ARF calculations. The monthly ARF values at surface ranged from −32 W m−2 to −46 W m−2, being larger in April and July than in the rest of months. The seasonal ARF evolution was inconsistent with seasonal aerosol optical depth (AOD) variation due to the effects induced by other aerosol parameter such as the single scattering albedo. The ARF at TOA changed from −9 W m−2 to −29 W m−2. Thus, the atmospheric ARF values (ARF at TOA minus ARF at surface) ranged from +15 to +35 W m−2. These results suggest that the African dust caused local atmospheric heating over the study location. The instantaneous aerosol radiative forcing efficiency (ARFE), aerosol radiative forcing per unit of AOD (440 nm), at surface and TOA during African desert dust events was evaluated according to the desert dust source origins. The ARFE values at surface were relatively high (in absolute term) and were −157 ± 20 (Sector A), −154 ± 23 (Sector B), and −147 ± 23 (Sector C) W m−2. These values were larger than many of the values found in literature which could be due to the presence of more absorbing atmospheric particles during African desert dust intrusions over our study area. Finally, our ARF computations showed good agreement with the corresponding ARF calculated by AERONET network.

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Single Scattering Albedo’s Spectral Dependence Effect on UV Irradiance

10.20944/preprints201806.0402.v1 ◽

2018 ◽

Author(s):

Ioannis-Panagiotis Raptis ◽

Stelios Kazadzis ◽

Kostas Eleftheratos ◽

Vassilis Amiridis ◽

Ilias Fountoulakis

Keyword(s):

Radiative Forcing ◽

Extinction Ratio ◽

Single Scattering ◽

Single Scattering Albedo ◽

Radiative Transfer Model ◽

Visible Range ◽

Transfer Model ◽

Uv Irradiance ◽

Visible Wavelengths ◽

Relative Differences

The Absorbing/scattering nature of aerosols affects the total radiative forcing and this absorption to total extinction ratio is quantified by single scattering albedo (SSA). Effect of SSA in the Ultraviolet (UV) irradiance is less studied and limited measurements are available. SSA retrieved at Athens, Greece during 2009-2014 from Ultraviolet Multifilter Radiometer (UVMFR) at 332 and 368 nm, were used to calculate incoming UV irradiance, alongside with ones from AERONET at visible wavelengths, from OMI satellite at 342.5 nm and from AEROCOM climatological database at 300 nm. UVA and UVB irradiances were estimated using a Radiative Transfer Model and we found that relative differences could be as high as 20%, while average relative differences varied from 2% to 8.7 % for the whole experimental period. Both UVA and UVB drop by a rate of ~12% for 0.05 aerosol absorption optical depth compared to ones estimated using SSA at visible range. Brewer irradiance measurements at 324nm were used to validate simulated irradiances and a better agreement was found when UVMFR SSAs were used with an average difference of 0.86%, while when using visible or climatological input, relative differences were estimated +4.91 and +4.15% accordingly.

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A Decade of Poland-AOD Aerosol Research Network Observations

Atmosphere ◽

10.3390/atmos12121583 ◽

2021 ◽

Vol 12 (12) ◽

pp. 1583

Author(s):

Krzysztof M. Markowicz ◽

Iwona S. Stachlewska ◽

Olga Zawadzka-Manko ◽

Dongxiang Wang ◽

Wojciech Kumala ◽

...

Keyword(s):

Optical Properties ◽

Radiative Forcing ◽

Research Network ◽

Radiative Transfer Model ◽

Chemical Components ◽

Transfer Model ◽

Aerosol Optical Properties ◽

Back Trajectories ◽

Aerosol Model ◽

Aerosol Radiative Forcing

The Poland-AOD aerosol research network was established in 2011 to improve aerosol–climate interaction knowledge and provide a real-time and historical, comprehensive, and quantitative database for the aerosol optical properties distribution over Poland. The network consists of research institutions and private owners operating 10 measurement stations and an organization responsible for aerosol model transport simulations. Poland-AOD collaboration provides observations of spectral aerosol optical depth (AOD), Ångstrom Exponent (AE), incoming shortwave (SW) and longwave (LW) radiation fluxes, vertical profiles of aerosol optical properties and surface aerosol scattering and absorption coefficient, as well as microphysical particle properties. Based on the radiative transfer model (RTM), the aerosol radiative forcing (ARF) and the heating rate are simulated. In addition, results from GEM-AQ and WRF-Chem models (e.g., aerosol mass mixing ratio and optical properties for several particle chemical components), and HYSPLIT back-trajectories are used to interpret the results of observation and to describe the 3D aerosol optical properties distribution. Results of Poland-AOD research indicate progressive improvement of air quality and atmospheric turbidity during the last decade. The AOD was reduced by about 0.02/10 yr (at 550 nm), which corresponds to positive trends in ARF. The estimated clear-sky ARF trend is 0.34 W/m2/10yr and 0.68 W/m2/10yr, respectively, at TOA and at Earth’s surface. Therefore, reduction in aerosol load observed in Poland can significantly contribute to climate warming.

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